Judith Zinspenning, the daughter of the Mennonite tradesman Conrad Zinspenning and Catharina de Mol, was married in 1652 to the physician Jacob Willemsz Sewel. She showed such a deep religious inclination that her father said: "It is a pity that this girl is not a boy, who then in time might become an eminent instrument in the church." Judith found the Flemish Mennonite worship dry and lifeless; the Collegiants were little better. In 1657 missionary William Ames won her to Quakerism. Here she found the lively inner "Spirit." The Sewels left the Mennonites and became ardent "instruments" of Quakerism. The Sewel home became a place for Quaker meetings. She was the first woman to lead worship services.

In 1663 she traveled to England with William Ames' successor William Caton, where she developed further intimate contacts with the Quakers. She preached and wrote several books, including Een ernstige Berispinge (An Earnest Reproof, 1660). She became a victim of a plague epidemic on her return to The Netherlands. Years later her son Willem Sewel published her writings in Eenige schriften en zendbrieven. . . nu tot verderen dienst gemeen gemaakt (1684). He also included a warm tribute to her in his Historie.